Blood warming devices have been used in multiple surgeries and trauma cases to warm blood or other physiological or crystalloid fluids to body temperature prior infusion. Blood warming devices are used to bring up the patient body temperature to a normothermic level during surgery or as a response to hypothermia.
Many blood warmers are based on the concept of warming the infusate as it flows through a heat exchanging means or a direct heating means embedded in the system. As the warmed infusate exits the heating system it flows through an intravenous tube accessing the patient. The intravenous tube is typically few feet long extending from the heating system with its distal end connected to the patient. The tube is generally exposed to the environment causing heat to be dissipated by convection.
The blood warmer described in U.S. Pat. No. 5,063,994 heats the blood as it flows to the patient through the intravenous line. This system has the advantage of avoiding any heat loss to the environment, but its warming means is limited to the surface area of the extruded plastic heat exchanger. This limitation impairs the effectiveness of this system and restricts its usage to the low flow applications
Many attempts were made to develop an effective blood warming system in combination with a thermally protected intravenous line to deliver warmed fluids at high and low flow rates. U.S. Pat. No. 5,417,274 combines a system having a heat exchanging means with a blood warming intravenous line to effectively warm infused blood. This system requires periodic maintenance because of its open system water tank.
The system described in U.S. Pat. No. 5,420,962 heats the infused fluid to the normothermic temperature inside the apparatus then utilizes a corrugated hose to envelope the intravenous line with a jet of hot air flowing inside. The hot air flows from the apparatus through the hose and exits out to the environment at the patient's end. The air hose protects the thermal integrity of the intravenous line, but the exiting flow of hot air to the environment is irritating to the patient and the surgeon. Moreover, the noise generated by the exiting air right at the patient's site is very annoying to the surgical staff.
U.S. Pat. No. 6,608,968 combines the heating of the blood as it flows through the system with the protection of the blood line from heat loss as it flows through the patient line. This method utilizes an elongated sleeve that is equipped with an electric heater. The sleeve is mounted on the warmed blood tubing as it exits the main heating module. The blood tubing has the same structure as the coaxial heat exchanger described in U.S. Pat. No. 5,063,994. In this configuration, the blood flows in the central channel that is surrounded by two half-donut channels. Still air in these outer channels act as an insulator preventing any heat loss from the blood in the central channel to the environment. The heating sleeve is awkward to use and increases the weight and the rigidity of the intravenous line that makes difficult to handle.
There is a need for an efficient fluid warmer for high and low flow rates, combined with a simple and effective intravenous line warmer to compensate for the heat loss at low flow rate, using a single low cost disposable set.